For interior heating and cooling, a filter for purifying indoor and outdoor air is implemented in the path of an airflow in an air conditioning duct for an air conditioning system.
Since the flow capacity of ducts differs due to cross sectional areas of the ducts differing from one another, a suitable filter is selected and used according to the characteristics of each duct. Generally, high-efficiency particulate air (HEPA) class dust filtration is used for dust collection, however, because this type of filtration is easily contaminated and quickly deteriorates due to retained contaminants of the filter, regular filter replacement is required for maintaining clean indoor air. The disposal requirement for spent filters incurs an expense and is a load on the environment.
In addition, with an increase in airflow through a filter, a loss of pressure increases, and a dust collection efficiency decreases. That is, with a high airflow in an air conditioning duct, an airflow through the filter also increases, thereby causing a loss of dust collection efficiency, a loss of pressure, and a consequent increase in the load on an air conditioning fan, and the result is a large air flow that cannot be handled by a filter having a small cross sectional area.
For these reasons, in order to handle a large airflow through an air conditioning duct, there is a problem in that the cross sectional area of a filter must increase, the cross sectional area of a duct must correspondingly increase, and so the overall space occupied by an air conditioning duct inside a building increases.